JPH03193328A - Thermoplastic resin stretched film and its manufacture - Google Patents

Abstract

PURPOSE:To provide the above film so that the film possesses uniform physical properties but bowing is little, by a method wherein heat shrinkable stress of a widthwise direction and a heat shrinkable factor of a widthwise direction of a thermoplastic resin stretched film which is oriented at least unidirectionally are specified. CONSTITUTION:A ratio sigma2/sigma1 of heat shrinkable stress sigma1 of a lateral (widthwise) direction of a film at a temperature higher by 70 deg.C than the glass transition temperature of the thermoplastic resin stretched film oriented at least in a lateral direction to heat shrinkable stress sigma2 of a lateral (widthwise) direction of the film at a temperature lower by 80 deg.C than the melting point should be 1.0 or less, preferably 0.9 or less. Then a heat shrinkable factor of a widthwise direction of the film is made into 5% or less at a temperature higher by 40 deg.C than the glass transition temperature. In addition, since the bigger a value of a ratio L/W of a length L of a cooling process for cooling of the film at the glass transition temperature or less between a lateral stretching and thermal fixation treatment to a film width W becomes, the more a reduction effect of a bowing phenomenon is improved, the ratio L/W is selected so as to become at least 1.0, preferably at least 2.0.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a stretched thermoplastic resin film with low bowing and having uniform physical and chemical properties in the width direction.

(Prior Art) Thermoplastic resin stretched films are used for packaging, industrial use, and other uses, and it is desirable that all parts of the film have the same physical property values.

However, in a normal transverse stretching method, the molecular orientation state is not the same between the center portion of the film and the side end portions of the film. The reason for this is that both ends of the film are gripped by clips in the tenter, and the stretching stress in the longitudinal direction (direction of travel of the film) generated by the stretching process and the shrinkage stress generated by the heat setting process are absorbed by the gripping means. While the film is restrained by the clips, the gripping means has less influence on the center of the film and the restraining force is weaker, and due to the above-mentioned stress, there is a delay in the center of the film compared to the ends gripped by the clips. is known to occur. When transverse stretching and heat setting are performed continuously in the same tenter, a straight line is drawn along the width direction (perpendicular to the direction of film travel) on the film before it enters the tenter. This straight line deforms inside the tenter and becomes convex at the beginning of the stretching process with respect to the film's traveling direction, returns to a straight line just before the end of the stretching process, and after the stretching process ends, it becomes convex. Deforms into a concave shape.

Furthermore, the concave deformation reaches its maximum in the middle of the heat-setting region, and the curve passes through the subsequent tenter with almost no change, leaving the concave deformation in the film that exits the tenter.

This phenomenon is called the bowing phenomenon, and the bowing phenomenon causes the physical property values of the film to become non-uniform in the width direction.

Due to the bowing phenomenon, the angle of the main axis of orientation tends to vary in the width direction of the film. As a result, physical property values such as longitudinal thermal contraction coefficient, thermal expansion coefficient, wet swelling coefficient, and refractive index differ in the width direction of the film.

Due to this bowing phenomenon, as an example of packaging applications,
Printed laminate KA2-1 This causes problems such as printing pitch deviation, unevenness, curling, meandering, etc. in the bag making process. Furthermore, as an example of industrial use, base films for floppy disks and the like cause problems such as poor magnetic recording characteristics due to in-plane anisotropy.

To explain in more detail, as a conventional technique in which a cooling process is provided between the transverse stretching process and the heat setting process, there is a
Publication No. 774 states that 20% of
A manufacturing method has been proposed in which a relaxation step at ~150° C. is interposed and a substantial cooling step is provided. However, the length of this cooling process is not described at all, and the effect of reducing the bowing phenomenon is also completely unknown. Furthermore, as a technology to reduce or eliminate the bowing phenomenon,
Japanese Patent No. 73978 proposes a film manufacturing method in which a group of nip rolls is installed between the transverse stretching process and the heat setting process. However, with this technique, the temperature of the intermediate zone where the nip rolls are installed is higher than the glass transition temperature, and the rigidity of the film at the nip point is low, so it is not very effective as an improvement measure.

Further, Japanese Patent Publication No. 63-24459 proposes a process in which a film after lateral stretching is held at both ends and forcibly moved forward only in a narrow area near the center using nip rolls. However, with this technology, it is necessary to install the nip roll in a high-temperature area within the tenter, and the roll and its peripheral equipment must be cooled. Also, since the film is at a high temperature, there is a risk of scratches caused by the roll on the film surface. , there are practical constraints. Also, special public service in Showa 6
No. 2-43858 discloses that after cooling the film immediately after transverse stretching to below the glass transition temperature, heat setting is performed in multiple stages.
Techniques have been proposed that involve heat fixation and simultaneous lateral stretching.

However, with this technology, the bowing reduction in the cooling process is small, or the bowing is likely to occur again in the heat setting process. It is a process. Therefore, there is a concern that it may be difficult to stably control the ambient temperature and film temperature within the tenter over a long period of time. Further, like Japanese Patent Publication No. 35-11774, this proposal also does not describe the length of the cooling process.

Furthermore, Japanese Patent Application Laid-Open No. 1-165423 proposes a technique in which a film after being laterally stretched is cooled to a temperature below the laterally stretching temperature, and then stretched again in the laterally direction while increasing the temperature in multiple stages. However, with this technology, as in the case of Japanese Patent Publication No. 82-43856, the reduction in bowing during the cooling process is small.
Or maybe it is because bowing tends to occur again during the heat setting process.
It is a complex process that includes a cooling process, multi-stage heat setting process, and re-stretching. Therefore, there is a concern that it may be difficult to stably control the ambient temperature and film temperature within the tenter over a long period of time.

Furthermore, although this proposal states that it is preferable for the length of the cooling process to be at least one-half of the film width, the basis for this is not clear, and the cooling process length and temperature at this level do not have the effect of reducing bowing. It is presumed that the company had to adopt a complicated process such as that described in L because of concerns that the amount of water would be low.
The publication proposes a technique for transverse stretching and heat setting by reversing the running direction of the film. However, with this technology, it is necessary to wind the film once to reverse the running direction of the film, and since it is an offline manufacturing method, there are problems such as productivity limitations. Attempts have been made to reduce this phenomenon, but these have all concerned manufacturing methods and equipment, and no inventions have focused on the properties of the film. For example, as seen in JP-A-58-215318 and JP-A-61-832E3, there is almost no deviation of the orientation principal axis at the center of the film width, regardless of the size of the bowing, and the extent of the bowing is In order to know this, seven samples of the entire width of the film were required, and it was impossible to determine the size of the bowing from a sample at any location on the film.

(Problems to be Solved by the Invention) The present invention relates to a stretched thermoplastic resin film that is industrially produced in large quantities and is made from thermoplastic as a raw material, and which has little difference in physical properties in the width direction. The objective is to provide an industrially advantageous manufacturing method.

(Means for Solving the Problems) In order to solve this problem, the present inventors have repeatedly conducted research and have found that a thermoplastic resin stretched film oriented in one direction has a The heat shrinkage stress (σ2) in the width direction at temperature is 100% or less of the heat shrinkage stress (σ, ) in the width direction at a temperature 70°C higher than the glass transition temperature, and the stress at a temperature 40°C higher than the glass transition temperature The inventors have discovered that a film with a heat shrinkage rate of 5% or less in the width direction has uniform physical properties with less bowing, leading to the present invention.

The present invention will be explained in detail below.

Thermoplastic resins applicable to the present invention include polyester resins such as polyethylene terephthalate, polyethylene 2,6-naphthalate, polyethylene isophthalate, and polyethylene terephthalate, polyamide resins such as nylon-6 and nylon 6.6, polypropylene, and polyethylene. Examples include polyolefin resins such as polyphenylene sulfide, polyethersulfone, polysulfone, polyetheretherketone, polyetherketoneketone, polyethylene trimellited imide, and many other simple substances, copolymers, mixtures, and composites. .

The thermoplastic resin stretched film oriented at least in the transverse direction of the present invention refers to a film that is stretched at least in the transverse direction at a stretching ratio of 2.5 times or more to impart molecular orientation to the film. Specifically, it may be a two-wheel oriented film in which a longitudinally stretched film that has been oriented in the longitudinal direction in advance is stretched in the transverse direction, or it may be a transversely or axially stretched film in which a substantially non-oriented film is oriented in the transverse direction. However, a two-wheel oriented film obtained by further stretching this transversely-axially stretched film in the longitudinal direction may also be used. In addition, after stretching the oriented film at least in the transverse direction, the temperature is 20° C. above the stretching temperature and above the melting point of the thermoplastic resin.
Heat treatment may be performed at a temperature between a low temperature and a low temperature.

The heat shrinkage stress (σ1.σ2) of the present invention is a value measured using the Vacuum Riko Co., Ltd. formula (%), and the heat shrinkage rate (H8TD) in the width direction of the film is 4
This is the value of the shrinkage rate in the width direction of the film when held at a temperature 0° C. higher for 30 minutes.

Also, although the reason is not clear, it is 70% lower than the glass transition temperature.
Thermal shrinkage stress σ in the transverse (width) direction of the film at high temperatures in °C
Lateral of the film at a temperature 80 °C below the melting point for 1 (
A film in which the ratio σ2/σ1 of the thermal shrinkage stress σ2 in the width direction is 1.0 or less, preferably 0.9 or less, has low bowing distortion and uniform physical properties in the width direction; Since the ing distortion increases, the value of σ2/σ must be small (both must be 1.0 or less).

When using the method of the present invention, when transversely stretching and heat-setting a thermoplastic resin film, the film before heat-setting is once cooled to below the glass transition temperature in order to reduce the bowing phenomenon that occurs during the transverse stretching process. The lower the cooling temperature, the more effective the reduction of the bowing phenomenon will be.

In addition, the larger the value of the ratio L/W between the length of the cooling process and the film width W, the more the effect of reducing the bowing phenomenon improves, and the L/W becomes larger.
It is preferable to select the length of the cooling process so that W≧2.0.

Here, the length of the cooling process is from the point where the temperature is substantially below the temperature of the previous process of the cooling process to the longest point immediately before reaching the temperature of the next process that is substantially higher than the temperature of the cooling process. The film width W means the distance between clips of the tenter at the outlet of the tenter. still,
The length of the cooling process and the film width W shall be expressed in the same unit, usually meters (m 2 ).

The present invention includes cases where two sheets are connected (transverse stretching, cooling, heat setting), re-horizontal stretching, re-longitudinal stretching, relaxation in the horizontal direction, relaxation in the longitudinal direction, fixed length width, etc. Of course, the case where at least one other -r factor exists is also included.

In addition, when separating the tenter that performs horizontal stretching and the tenter that performs heat setting, the film is cooled because it is run in the atmosphere, so the ratio of the length of the cooling process to the film width W is correct. The present invention also includes performing lateral stretching and heat setting using separate tenters, as long as the scope of the patent claims is substantially expanded.

(Example) Next, the present invention will be explained in more detail based on Examples, but the present invention is not limited to the following examples unless it exceeds the gist of the invention.Example 1 Polyethylene terephthalate resin After melting and extruding through a T-die and forming into a film on a chill roll, it was stretched 3.6 times in the longitudinal direction with a roll stretching machine, then 3.7 times in the transverse direction with a tenter, and heat-set biaxially. It was made into an oriented polyethylene terephthalate film. In the tenter, the film is preheated at 90°C, then stretched at 100°C, then the film is cooled once at 55°C with a length of L/W = 1.0, and then the film is stretched at 220°C. After heat treatment at 200℃ and further heat treatment at 200℃,
The film was cooled to 00°C. I then removed it from the clip and wound the film as usual.

Example 2 A biaxially oriented polyethylene terephthalate film was obtained in the same manner as in Example 1 except that the ratio of the length of the cooling process to the film width W (L/W) was 3.0. Ta.

Example 3 Polyethylene terephthalate resin was melted and extruded through a T-die, formed into a film on a chill roll, stretched 3.7 times in the transverse direction at 100°C with a tenter, and then stretched 3.7 times in the machine direction with a roll stretching machine. After stretching 6 times, the film was tentered four times, heat-treated at 220°C, further heat-treated at 200°C, and then cooled to 100°C to obtain a biaxially oriented polyethylene terephthalate film. I then removed it from the clip and wound the film as usual. In addition, between the transverse stretching process and the heat setting process, the ratio (L/W) of the length of the cooling process at 65°C or less and the film width W is substantially 5.0 or more.
1).

Comparative Example 1 In Example 1, no cooling step is provided (L/W=0)
A biaxially oriented polyethylene terephthalate film was obtained in the same manner as in Example 1 except for this.

Comparative Example 2 A two-wheel oriented polyethylene terephthalate film was obtained in the same manner as in Example 1, except that the ratio (L/W) between the length and film width W in the cooling step was 0.5.

Example 4 Nylon-6 resin was melted and extruded through a T-die, formed into a film with a chill roll L, stretched 3.25 times in the longitudinal direction with a roll stretching machine, and then 3.5 times in the transverse direction with a tenter. A biaxially oriented nylon-6 film was drawn and heat set.

In the tenter, the film was preheated at 60°C, then stretched at 85°C, and then the film was stretched to L/W=3.0.
The film was then heat treated at 235°C, and after a further heat treatment at 210°C, the film was cooled to 100°C. I then removed it from the clip and wound the film as usual.

Comparative Example 3 In Example 4, no cooling step is provided (L/W=0)
Biaxially oriented nylon-6 was prepared in the same manner as in Example 4 except for
I got the film.

The ratio of each heat shrinkage stress of the films of Examples and Comparative Examples (σ2/
σI), the heat shrinkage rate in the width direction (H8tn) and bowing strain (B) at 40"C below the glass transition point temperature are shown in the table. The bowing strain is calculated by drawing a straight line on the surface of the film before entering the tenter. , the first on the final obtained film
The ratio between the bow-shaped deformation ffi (b) and the film width as shown in the figure is expressed as a 6th ratio (100b/W).

In addition, the ratio of each heat shrinkage stress (σ2/σI) and the heat shrinkage rate in the width direction at 40°C from the glass transition point temperature (HS TO)
shows those values in the central part of each film.

In the following margin comparison example 1.2, the value of (σ2/σ,) is larger than 1,
In this case, a significant bowing phenomenon occurs and production is hindered, which is a problem outside the scope of the claims of the present invention, but the thermoplastic resin stretched film obtained by the present invention has a uniform shape in the width direction with less bowing. It can be seen that it has physical properties.

(Effects of the Invention) According to the present invention, a thermoplastic resin film having uniform physical and chemical properties in the width direction can be obtained, and the film is extremely useful for packaging, industrial use, and other uses. I understand.

[Brief explanation of drawings]

Figure 1 shows the calculation method for Boeing distortion.

Claims (2)

[Claims] (1) The heat shrinkage stress in the transverse direction of the film satisfies formula (1), and the heat shrinkage rate in the transverse direction at a temperature 40°C higher than the glass transition temperature is 5% or less, and the heat is oriented in at least one direction. Plastic resin stretched film. (σ_2/σ_1)≦1.0...(1) In equation (1), σ_1 is the lateral heat shrinkage stress of the film at a temperature 70°C higher than the glass transition temperature,
σ_2 means the transverse thermal shrinkage stress of the film at a temperature 80° C. below the melting point. (2) The heat shrinkage stress in the transverse direction of the film satisfies formula (1), and the heat shrinkage rate in the transverse direction at a temperature 40°C higher than the glass transition point temperature is at least 5% or less. When producing a stretched plastic resin film, a cooling process of a length satisfying the formula (2) is provided between the transverse stretching process and the heat setting process to cool the film to below the glass transition temperature. A method for producing a stretched plastic resin film. (L/W)≧1.0 (2) In equation (2), L means the length of the cooling process, and W means the film width.